VI presentation 09 2003

Vibration Case Histories Barry T Cease MeadWestvaco 9/19/2006 Introduction Case History#1 – Excessive Vibration Of Motor  Case History#2 – Strange Motor & Gearbox Vibration  Case History#3 – Repeat Fan Bearing Failures  Case History#4 – Pump Bearing Cage Failure  9/19/2006 Case History#1, Excessive Vibration Of Motor EQUIPMENT: Nash 9000 series vacuum pump driven by a single reduction, parallel gearbox and a 700 HP synchronous motor  The vacuum pump is one of many used to pull water out of the paper (dry it) as it moves thru the process  9/19/2006 CH#1 – Equipment Layout 9/19/2006 CH#1 - Problem Excessive & noisy vibration at motor  This problem could be heard & felt clearly at the motor  It sounded like something was rubbing and/or loose  9/19/2006 CH#1 – Test Data & Observations (Motor) Motor speed was exactly 400 rpm  Pump speed was 267 rpm  Pump vibration data showed no abnormal patterns or levels  Motor spectra showed many harmonics of running speed and of 133 cpm (1/3 x rpm)  Motor waveform showed impacting at 400 & 133 cpm  9/19/2006 CH#1 - Motor Spectra 9/19/2006 CH#1 – Motor Spectra Zoom 9/19/2006 CH#1 – Motor Waveform 9/19/2006 CH#1 – Test Data & Observations (Gearbox)       Gearbox input speed was 400 rpm Gearbox output speed was 267 rpm (1.5:1 ratio and 56T/84T) Gearbox spectra showed many harmonics of both input & output speed and 133 cpm (1/2 x output) Gearbox spectra didn’t show high gearmesh frequency at 22,400 cpm Gearbox waveform showed heavy impacting at 400 cpm Gearbox Peakvue data showed many harmonics of 400 cpm 10 9/19/2006 CH#3 – Fan Trend Data 42 9/19/2006 CH#3 – Test Data & Observations, Part The fan bearings were standard pillow block style housings with tapered roller bearings inside  We assumed these were selfaligning bearings as most pillow blocks are, but this assumption turned out to be false  43 9/19/2006 CH#3 – Conclusion & Recommendations, Part    The relatively tight alignment tolerances of the existing tapered roller bearings combined with the poor condition of the fan base made for short bearing life We asked our bearing supplier for a replacement bearing type that would carry the same load, but be more forgiving for misalignment We also had our machine shop fabricate a new fan base that was machined flat & line bored to perfectly fit the new pillow block bolt pattern 44 9/19/2006 CH#3 – Conclusions & Recommendations, Part    After installation of the new type bearings & new fan base we have not had another bearing failure Our bearing life has went from an average of 4-months to 26 months and counting Further inspection of maintenance history showed a fan speed increase which corresponded quite well to our increased rate of failure 45 9/19/2006 CH#3 – Conclusions & Recommendations, Part    This case history is a good example of both predictive & proactive maintenance Predictive maintenance allowed us to avoid catastrophic fan bearing failures and perform repairs during scheduled outages Proactive maintenance extended the life & reliability of the fan bearings 46 9/19/2006 Case History#4, Pump Outboard Bearing Cage Failure Equipment: Double-suction, centrifugal pump driven by a 1250 HP synchronous motor turning at 514 rpm  This is the most critical pump in the process directly providing the product (stock) used to make paper on the paper machine  47 9/19/2006 CH#4 - Problem  Increasing HFD vibration levels at pump outboard Current levels had exceeded maximum of long term trend 48 9/19/2006 CH#4 – Test Data & Observations, Part Since the bearing was oil lubricated, an analysis of the outboard bearing oil was requested  Oil analysis results showed very high copper levels indicating cage wear  Vibration data showed very high HFD levels on outboard bearing  49 9/19/2006 CH#4 – HFD Trend 50 9/19/2006 CH#4 – Test Data & Observations, Part Peakvue spectra showed harmonics of fundamental train frequency (cage)  An 10/01 paper by J Robinson & J Berry recommends a Peakvue fault level of 4.0 g’s pk-to-pk for a 500 rpm machine  Peakvue waveform on outboard bearing showed levels at 11.3 g’s pk-to-pk!!!  Maintenance history showed a continuing problem of a leaking pump outboard seal  51 9/19/2006 CH#4 – Peakvue Spectra, P1 52 9/19/2006 CH#4 – Peakvue Spectra, P2 53 9/19/2006 CH#4 – Peakvue Waveform 54 9/19/2006 CH#4 – Conclusion & Recommendations, Part The recommendation was made to changeout the pump outboard bearing  Later inspection of the bearing showed the cage worn badly particularly in the area separating the rolling elements from one another  During the bearing change, shims were found under the bearing making up the fit with the housing  55 9/19/2006 CH#4 – Conclusion & Recommendations, Part      Failure analysis of the bearing found lube contamination and skidding as the primary causes of failure Corrective actions were as follows: 1) Replace the outboard bearing housing, 2) Repair or replace the pump outboard packing gland, 3) Replace the pump rotor which was causing thrust loading, and 4) Upgrade the lube from an ISO 68 to an ISO 150 weight oil (temporarily use grease until packing gland repaired) 56 9/19/2006 ...Introduction Case History#1 – Excessive Vibration Of Motor  Case History#2 – Strange Motor & Gearbox Vibration  Case History#3 – Repeat Fan Bearing Failures  Case History#4... gearbox was changed in 8/02  After motor change in 7/02, motor vibration levels initially dropped, but eventually resumed previous levels  The gearbox installed in 8/02 had been used before,... thru the process  9/19/2006 CH#1 – Equipment Layout 9/19/2006 CH#1 - Problem Excessive & noisy vibration at motor  This problem could be heard & felt clearly at the motor  It sounded like something